How can you tell if a child is faking a tic disorder?

Monitor / film: Although some kids with tic disorders (under stress) can supress them to some degree, they often rebound with greater tic activity when no one is watching. One cool observation shows that kids under 8 or so are not aware of peripheral vision. If you monitor their tic behavior when they don't think you are looking it should stop in the fake. A videocam surveylance would give similar data.

Not sure it matters: It would be fairly unusual for a child to persistently "fake" a motor or vocal tic, expect perhaps to bug siblings or parents. If a child is recurrently exhibiting tics but only when there's someone around to bug, it might be "fake, " but its still a problem. Tics per se are not dangerous, so waiting a watching is a reasonable first step.

Goes away in sleep: Tics disappear in sleep. If your child pretends to be asleep and continues to have tics they are not organic. Should see a psychologist to analyze the situation of pretended tics.